RHEOLOGICAL PROPERTIES OF MALTODEXTRINE GELS

Lucyna Słomińska, Wojciech Krzyżaniak, Karolina Stempin

ABSTRACT

The relationships between structural-mechanical properties of maltodextrine gels texture have been presented in this paper. The study shows substantial differences of the observed features between the industrial (Nowamyl) and laboratory maltodextrines (ME1 and ME2). Values of parameters such as strength, adhesion, ductility, and gumminess were higher for Nowamyl than for ME1 and ME2. In spite of a similar value of DE, industrial maltodextrine was harder and presented greater adhesion than ME1 and ME2 maltodextrines. The positive correlation between concentration and gel strength of all tested maltodextrines was observed. However, unessential influence of pH was indicated only for Nowamyl.

Key words: maltodextrine, rheology, gels, texture, reference surface, hardness..

INTRODUCTION

Texture is a sensorial reflection of food structure and the way in which it reacts for applied forces [11]. Very specific is the way texture is created in product. It is produced during process in situ and as a result of many technological procedures which are aimed on its creation and modification. The most typical texture features are: fragility, brittleness, delicacy, succulence, firmness, and features that are not accepted include: fibrousness, sogginess, wateriness, breaking up, lumpiness and mucinosis [13]. It results from texture definition that has a sensorial nature. Therefore, it is natural to apply sensorial analysis methods in the investigations of texture features.

Quantitative descriptive analysis QDA is one of sensorial methods used in texture research. The most effective result of measurements could be obtained by carrying out texture profile analysis [1, 3, 10].

Other approach to sensorial research of texture is consumer-moulding method [15].

However, these investigations have quite big amount of disadvantages. This is the reason by instrumental methods have been applied for many years. There are three types of them: basic, empirical and imitating ones. [9, 14].

Basic tests allow to collect for carrying out empirical tests. Regarding the kinds of forces acting on a sample these tests can be divided into following tests: penetration tests, compressions and extensions tests, cutting off and crossing tests, viscosimetric pressing tests [17, 18, 19].

Imitating tests imitate conditions existing in mouth or during preparation of food for consumption. One of the first such instruments was a tenderometer described by Volodkevicha in 1938. The principle turn in instrumental texture research was made with the introduction of the General Food's textorometer. It allowed elaborating of decorating texture method in an instrumental version of TPA. The greatest advantage of a described method is a very high correlation of obtained results with sensorial estimation [12].

The important step in dissemination of TPA method was its adopting in 1968 by Bourne for universal testing apparatus - Instron [2, 8].

Other solution is the use of Voisey's texture measurement system: Ottawa (OTMS) [20]. The latest texture research is based on connecting face muscles or man's palate to electronic measurement elements. Collected electric impulses, after converting, permit to analyze texture properties in an objective manner (electromiography-EMG) [7].

The aim of research was instrumental characterization of distinguishing texture features of experimental maltodextrine gels obtained by the way of extrusion and their comparison witch commercial maltodextrine obtained by traditional method application.

MATERIALS AND METHODS

Substrate
The following experimental maltodextrines were used as a substrate for research: extrudated with BAN 480 L enzyme (Novo Nordisk) maltodextrin (marked as ME1) and extrudated with Gamalpha 300 L enzyme (Gama Chemie) (marked as ME2). Commercial maltodextrine Nowamyl (produced by a Polish company – PPZ Łobez) was used as a comparison.

In these substrates the following analysis were carried out: dry substance [PN-78/A-74701], the amount of reducing groups by modified Schoorl-Rogenbogen method [PN-78/A-74701], solubility by Leach method [6], carbohydrate composition by High Performance Liquid Chromatography. HPLC apparatus Agilent 1100 Series was used with Aminex HPX 42A column (7.8 x 250 nm), Bio-Rad. The elution of carbohydrate was detected with a differential refractometer (HP 1047A Ri). Samples (20 µl) were injected into the column and eluted with water at 85°C at a velocity 0,6 ml/min, the iodine absorbance value was defined as the optical density at 500 nm using a 4 cm cell in Pye Unican SP500 Series 2 spectrophotometer.

Preparation of experiment
15, 17.5, 20, 25 and 30% concentrations of maltodextrines were made. They were heated up to 60-70°C while stirring. After a complete dissolution maltodextrines were cooled down to 40°C. The appropriate pH levels were fixed: 4.0, 6.0, 8.0 (with 10% concentrated citric acid or 10% concentrated sodium chloride). Than maltodextrines were stored in temperature 5, 15, 25°C for 24 h.

Texture Profile Analysis was made in samples. The test involved compressing the sample twice in a reciprocating motion with continuous registration of force.

The interval between the first and the second measurement was 5 s. The sample was cylinder shape, 4 cm in diameter and 4 cm high. Texturometer TA.XT 2i Stable Micro Systems with 5 kg load cell was used. The sample was penetrated with a cylinder head, 1 cm in diameter and 2 cm high. Before measurement samples were stabilized in a room temperature for one hour. This was done to achieve compensation of temperature in all samples. Main parameters of measurements were: penetration depth 15.0 mm, pre test speed 1 mm/s, test speed 0.5 mm/s, post test speed 1 mm/s.

The following experimental factors of TPA (independent variables A, B, C) were taken: A storage temperature 5-15-25°C, B pH: 4.0-6.0-8.0, C concentration 15-17.5-20% (extrudated maltodextrines) and 20-25 -30% (Nowamyl).

Real level values of factors, presented above, correspond to coded values: -1, 0, 1, where -1 and 1 are adequately the lowest and the highest values of factors, however, 0 corresponds to the middle of studied range that is middle level. The three-level factorial system with 17 measurement points was chosen. The control point coded ac 0,0,0 was done with 5 repetitions.

Statistical analysis of the results
One-way analysis of variance was made to state if there were any significant differences between average values and examined samples. Calculations were made at the a = 0.05 level. Tukey's test was also carried out to state which pairs of examined average values were the highest differences.

A method of reference surface in the experiment's optimisation was applied. One of the conditions necessary for correct caring out of an experiment with satisfactory results was to draw up an experiment plan. It was based on the diversity of independent variables experiment factors for the qualification of their influence on dependent variables.

The application of optimal experiment plans allowed getting a lot of easy to interpret data from a few experiments and to determinate optimal level of independent variables as well as determinate interactions between those factors.

The method of reference surface made it possible to create an experiment plan. This method was based on making specific number of experiments and enables to study the influence of several factors simultaneously. Based on obtained results one could specify the essentiality of appointed factors on researched references and the essentiality of interactions between researched factors. For the optimisation of the process, dependences between factors could be presented as mathematic equations [4].

RESULTS AND DISCUSSION

Substrate characteristics
Dry substance of maltodextrines ME 1 I ME2 amounted respectively 89.4% and 88.5%. Moisture of maltodextrme Nowamyl was 91.5%. These differences came from different conditions of product drying. Commercial maltodextrine was sprayed dried at temperature 180-200°C but experimental maltodextrine was convection dried at temperature 80°C for 24 h. DE values of ME1, ME2 and Nowamyl were almost the same and amounts respectively: 4.5; 3 and 5. It made it possible, in further research, to compare gel properties of these maltodekstrines.

The best solubility was indicated by commercial maltodextrine - 99%, while the solubility of ME1 was 74% and ME2 was 80%. High Nowamyl's solubility was correlated with its low iodine value. It was three times lower than iodine value for experimental maltodextrines (Table 1).

Chromatographic analysis showed substantial differences in maltodextrines carbohydrate composition (Table 2). The highest amount of DPn 92.5% had ME2. The percentage of higher sugars for Nowamyl and ME1 were similar and resulted respectively in: 85%, 82.5%.

Higher amount of carbohydrates DP6-8 and lower glucose content in comparison to experimental maltodextrines characterized commercial maltodextrine.

The comparison of ME1 and Nowamyl carbohydrates composition allowed noting that kind of hydrolyse influences quantitative carbohydrates content. In case of extrusion application amount of carbohydrates DP1-DP8 oscillated from 1.7 to 2.4%. Traditional hydrolyse performed small differences between DP7-DP8 and DP1-DP2 (3%).

Comparison of selected texture profile features
Experiments were carried out at the same parameters of starch concentration, temperature and pH. Maltodextrine samples were characterised by different ability of gel creation, which was dependant on starch concentration. In case of ME1 and ME2 gels were created at 15% starch concentration and Nowamyl gels were made when starch concentration were higher than 20%.

For an objective TPA comparison of investigated samples the 20% starch concentration, at 15°C and pH 6 samples were made.

One-way analysis of variance and Tukey's test HSD were made. Conclusions were made at the a = 0.05 level. Significant differences between commercial and experimental maltodextrines were considered. Hardness, adhesiveness, ductility, gumminess were substantially higher for Nowamyl than for ME1 and ME2 (Table 3).

Hardness, which was indispensable for occurring the determined deformation in the case of commercial maltodextrine, was 2.5 to 2.6 times higher than in case of experimental maltodextrines. The adhesion of ME1 and ME2 was on average 7.5 times lower than Nowamyl adhesion. However, gumminess and ductility of experimental maltodextrines were 3 times lower than of commercial maltodextrine.

Values of cohesiveness, springiness and return springiness were higher for ME1, ME2 than Nowamyl. Cohesiveness, which represents internal binding force, was near the same for ME1 and ME2 but for Nowamyl it was lower by 0.13 to 0.15 units.

Springiness and return springiness were the speed measurements of material returning to original form. These both texture features were higher for maltodextrine produced by extrusion. On the base of investigations a conclusion was made that commercial maltodextrine was characterized by very high solubility and that high carbohydrate content of DP6-DP8 was harder and indicate higher adhesion to measurement element than experimental maltodextrines.

Ductility and gumminess of Nowamyl connected with hardness and carbohydrate composition of maltodextrines were considerably different than for experimental maltodextrines.

Low value of adhesion for ME1 and ME2 combined with high cohesion caused the creation of concise gel as opposed to harder but less concise gel made from Nowamyl.

Inverted proportion of adhesiveness and cohesiveness for Nowamyl created gel that strongly covered measurement element.

The characteristics of equations of reference surface for discriminates of texture profile – force
The influence of experimental factors on selected parameter of texture profile for ME1, ME2 and Nowamyl was determined on the base of figures and equations of reference surface. Table 4 shows equations of reference parameters for Nowamyl, ME1 and ME2 hardness. In order to present an influence of all examined factors for coded values 0,0,0 of independent variables suction reference surface were used.

They make it easier to compare quantities' influence of the rage for each experimental factor.

Nowamyl
Reduced square model with high value of corrected coefficient of determination (corr r² = 0.99) was chosen for Nowamyl.

Maltodextrine concentration and temperature had the greatest influence on gel hardness. pH had insufficient influence. Strong positive correlation between concentration and gel hardness was noticed. Temperature and hardness was characterized by negative correlation. These statements were correct when remaining factors were on level 0 (Fig. 1).

The highest hardness value was observed for 30% concentrated gel at 5°C and the lowest for 20% concentrated gel at 25°C. It shows that hardness which is needed for breaking of gel structure increases with a simultaneous temperature decrease and concentration increase (Fig. 2).

ME1
For ME1 together with concentration increase to the level corresponded with code variable value 0 the increase of hardness was observed. After exiting this value, the decrease was observed. Maximum and similar hardness values were in samples with minimal and maximal pH and temperature. The lowest durability occurred in gel at temperature and pH on 0 level. These statements were correct when remaining factors were on level 0 (Fig. 3).

Essential influence on examined gel hardness was for simultaneous action of temperature and maltodextrine concentration as well as for pH and maltodextrine concentration. Referenced surfaces were similar for both cases.

The highest durability was observed for gels with 15% and 20% concentrated maltodextrines at temperature and pH on minimal and maximal values level (Fig. 4 and 5).

ME2
For ME2 the concentration increase caused the hardness increase. Temperature and pH were negatively correlated with hardness. The most essential influence was observed for temperature and then for concentration. All gels with concentration above 18.5% had similar durability (Fig. 6). The highest hardness value was observed for samples with pH 4 and stored in temperature 5°C (Fig. 7). Between temperature and concentration there was an essential interaction that was stronger for 20% concentrated gels. The temperature increase caused the decrease of gel endurance. (Fig. 8).

It allowed coming to conclusion that positive correlation existed between temperature and concentration for gel hardness of all delaminated maltodextrines. However, pH had not any influence for gel hardness made from Nowamyl.

CONCLUSIONS

1. Sufficient differences between commercial maltodextrine and experimental maltodextrines were observed. Hardness, adhesiveness, ductility, gumminess were considerably higher for Nowamyl than for ME1, and ME2. However, cohesiveness, springiness and return springiness were higher for ME1 and ME2.
2. Nowamyl in spite of similar DE value was significantly harder than ME1 and ME2. These differences probably resulted from carbohydrate composition and distinct methods of the preparation of maltodextrines.
3. Temperature and concentration significantly influenced on maltodextrine hardness. The influence of pH was unessential.

This study has been carried out with financial support from the State Committee of Scientific Research (grant PBZ-KBN 021/P06/13/2001).

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